Master valve lock for servomotors



Feb. 15, 1944. ws 2,341,696

MASTER VALVE LOOK FOR SERVOMOTORS INVENT OR ERNEST DAVIS ATTORNEYS kM/MM Feb. 15, 1944. E, DAVIS 2,341,696

MASTER VALVE Locx FOR SE'RVOMOTB S I Filed June 9, 1942 3 Sheets-Sheet 2 FIG. 5

20 FIG. 2

2 HH HI 3| 3 32 d E 36 I Bo h HRH 9 37 B INVENTOR ERNEST DAVIS fiaMMrW ATTORNEYS Feb. 15, 1944. v E. DAVIS 2,341,696

MASTER VALVE LOCK FOR SERVOMOTORS Filed June 9. 1942 3 Sheets-Sheet 5 INVENTOR E R N EST DAVIS BY Mama ATTORNEYS ton has traveled a predetermined distance.

Patented Feb. 15, 1944 MASTER VALVE nocxron SERVOMOTOBS Ernest Davis, Syracuse, N. Y., asslgnor to The Prosperity Company, Inc., Syracuse, N. Y., a

corporation or New York Application June 9, 1942, Serial No. 446,388

12 Claims.

This invention relates to means for locking the master valves for servo-motorsin their operated position, and has for its object a lock controlled in its operation by the movement of the servomotor or some part operated thereby, and release means which, when operated, immediately releases the master valve and prevents any unintentional repeated operations by the re-action of the pressure fluid in theiiuid power system or by the rebuilding of pressure due to lag in exhaust when the manual exhaust valve is momentarily operated instead of being held open an appreciable time.

This valve lock is particularly applicable to locking the master valves of machines having an opening and closing movement, such as garment and laundry presses after the master valve has been initially opened by the operator, as by operating a two hand control where the master valve is timed and locked and by the operation of the motor or the machine which the motor serves. The valve lock usually is timed to operate when the machine is nearly closed.

The valve lock is here shown as applied to the servo-motor of the single acting cylinder and piston type and is operated by air pressure from the cylinder or from a port in the side of the cylinder arranged to be uncovered after the pis- In such machines, the master valves have been held in uniocked position by a diaphragm, which is actuated by the delayed pressure passing to the diaphragm chamber after the machine served by the motor has operated or closed to a predetermined extent. To open such machines, the air is exhausted from the diaphragm chamber and the air exhausts back through the feed pipe to erate the master valve, when the piston is only part Way back in its retrograde movement. Such operation of the diaphragm results in the machine immediately closing again with danger to the operator.

The object of this invention isto take the locking operation away from the diaphragm and to effect the locking operation by a. pressure-operated valve member, which may be released upon merely a touch of the release lever, and which, when initially released, opens up the chamber in which the valve is located to an open exhaust, in addition to the exhaust through the pipe, which ordinarily leads from the port in the side of the cylinder, so that the danger of unintentional repeated operation is eliminated.

The invention consists in the novel features and in the combinations and constructions hereinafter set forth and claimed.

In describing this invention, reference is had to the accompanying drawings in which like characters designate corresponding parts in all the diaphragm chamber, permitting the master f valve to close its intake and also open its exhaust, the master valve being usually of the combined intake and exhaust type. In such installations, the operator should hold the release valve open for a predetermined time sufficient for the piston of the servo-motor to pass the port in the side of the cylinder, when the piston is on its retrograde movement. The retragrade movement, as will be understood, may be effected by countersprings. However, oftentimes the operator does not hold the release lever long enough, and hence the release valve would close before the piston head again passed the port on its retrograde movement, so that, although the exhaust of the master valve is open, the air on. the pressure side of the piston in the cylinder would again build up the views.

Figure 1 is a vertical sectional view through the master valve, a two hand control mechanism being also shown, and the contiguous portion of the servo-motor being shown.

Figure 2 is a view showing the master valve in Figure l in its operated position.

Figure 3 is an end view of a modified form of the master valve and locking means therefor.

Figure 4 is an elevation partly in section looking to the right in Figure 3.

Figure 5 is sectional view on line 5-45, Figure 4.

The invention comprises a pressure-operated device, as a diaphragm in a diaphragm chamber, for opening a master valve which controls the flow of pressure fluid, as air, from a suitable supply system to a servo-motor, pressure-operated means for holding the master valve in its operated position independently of the pressure-operated device or diaphragm, the flow of pressure fluid to the locking means being timed and controlled by the movement of the movable member or piston of the servo-motor, or some part operated thereby, this locking means including a valve of the poppet type located in a pressure chamber and normally spaced from and its seat by the pressure in the chamber in which the locking valve is located, the diaphragm being constructed so that the air leaks therethrough sufiicient pressure on the diaphragm to again opafter the diaphragm has been given an initial impulse to open the master valve, so that the diamaster valve is concerned, the chamber in which the locking valve is located having an exhaust to the outer air, which is closed of! by the seating of the locking valve and which is'immediately opened to the exhaust of air upon the starting of the-unseating movement of the locking valve, together with operator-releasable means, as an exhaust valve, for opening the chamber in which the locking valve is located, to the exhaust of air therefrom, so that upon initial opening of the operator-operated release valve, the air immediately releases and the master valve operates to cut oil! the servo-motor to the flow of air therethrough and to exhaust it to the outer air. The master valve is of the combined intake and exhaust type with its intake normally closed and its exhaust normally open, and owing to the locking valve, it is merely necessary for the operator to momentarily open the exhaust valve and not necessary to hold it open, as immediately upon the opening of this operator-operated exhaust valve, the locking valve unseats to open the locking valve chamber to the exhaust of air through the passage closed by the exhaust valve, when seated.

Two forms of the invention are shown. In Figure 1, one diaphragm, as I4, is used to both open the master valve and move the locking valve toward its seat before the chamber in which the locking valve is located, receives air pressure controlled by the servo-motor. In Figures 3, 4, and 5, one diaphragm is usedto open the master valve, when the manual control, as two hand control, is operated, and another diaphragm, as 50, used to initially move the locking valve against its seat, this diaphragm being of pervious material to permit the air to filter therethrough and apply pressure to the head of the locking valve and hold it'against its seat, so that the pressure equalizes on opposite sides of the diaphragm, and the pressure holding the valve against its seat is applied directly to the head of the locking valve, after this valve has been seated. In both instances, the opening of the release valve, opens the exhaust to the chamber or space having the seat for the locking valve, permitting the valve to immediately unseat and open such chamber or space to the exhaust of air without the necessity of holding the operator-operated release valve open. The pervious quality of the material or the construction of the diaphragm to permit the air to pass therethrough after the diaphragm has been given an operating impulse, is shown as a small leak port l4.

In the form shown in Figures 1 and 2, the diaphragm I4 is also pervious, as the air pressure applied to one side thereof to give the impulse thereto upon the operation of the manual or two hand control, filters through the diaphragm and exhausts to the outer air, so that this diaphragm becomes inert after-the locking valve seats.

In both instances, any back build up of pressure, after the release valve has been operated,

can not build up to operate the master valve, and cause repeated operation, upon one operation of the manual or two hand control.

I designates the master valve as a whole, this being of the combined intake and exhaust type and having a casing 2 and a movable valve member 3 therein provided with a normally-closed intake valve head 4 and a normally-open exhaust valve head 5 connected together to act as a unit. The valve member 3 is self-returnable, it being acted upon by a suitable spring I to return it to its normal position. The intake end 01 the valve casing 2 communicates with anintake pipe I. for

a pressure fluid, as air. The exhaust end of the casing has an exhaust passage 8 to the outer air controlled by the valve head 5. The intermediate part or the casing 2 between the heads of the valve, as 4, 5, is provided with a pipe 9 to the.

intake end of the cylinder ID of the servo-motor. The cylinder has a port I I in the side thereof. arranged to be passed by the piston II, when the piston has been actuated a predetermined distance on its power stroke. The piston rod I3 is connected to suitable motion transmitting mechanism to effedt the operation of the machine, as to effect the operation of the press head 01' a pressing machine. The piston is single acting and is returned by counter-springs or weights embodied in the machine to which the servomotor is applied.

The means for operating the movable member 3 of the master valve to open the intake valve head 4 and close the exhaust valve head 5 is here shown as a pressure-operated device, as a diaphragm located in a diaphragm chamber with the flow of pressure fluid, as compressed air, to the pressure side of the diaphragm being controlled by a two hand control. l4 designates the diaphragm located in the diaphragm chamber IS, the diaphragm acting on the valve member 3 through yielding means, as a spring l6, to close the exhaust valve head 5 of the master valve and open the intake head 4. The spring thrusts at one end against the diaphragm or a disk ll, reinforcing the central portion of the diaphragm, and against the bottom of a hollow abutment l8 slidably mounted in the valve casing and thrusting against the exhaust valve head 5. The spring thus tends to return the diaphragm to starting position. The valve head 5 has a stem 19 extending axially into the abutment I8 through the head of the abutment, so that the exhaust valve head 5 is centered in its shifting movement. The diaphragm is of a porous material or has a small leak port therethrough instead ofbeing tight, and hence the air slowly exhausts or leaks out of the pressure side of the diaphragm chamber after the diaphragm has been given an operating impulse by a sudden rush of air when the control valves are operated. In short, after the operating impulse, the diaphragm is disabledby the leakage of air through the diaphragm. The air for operating the diaphragm enters the diaphragm chamber l5 from a pipe 20 connected to the main line air conduit 1 through a pair of manually-operated valves connected in series between the pipe 20 and the pipe 1.

2| designates the two hand control valves. Each is of the combined intake and exhaust type having a normally-closed, spring-pressed intake valve head 22 and a normally-open exhaust valve head 23. The intake end of one control valve casing is connected by a pipe 24 to the main intake pipe I, the outlet of this valve being connected by a pipe 25 to the intake end or the other valve casing. The latter valve casing communicates with the diaphragm chamber it through the pipe 20. The construction 01 the two hand controls form no part or this invention, and any suitable two hand control mechanism may be used. The movable valve members of the two hand control valves are operated by manuals 26. When both manuals 26 are operated, the air flows from the main line 1 through the valves 2| and pipe 20 to the diaphragm chamber, actuating the diaphragm l4 from the position shown in Figure 1 to that shown in Figure 2, thus opening the intake head 4 of the master valve and closing the exhaust valve head 5, so that the air passes from the main pipe I through the master valve 2 and pipe 9 to the cylinder ID of the servomotor to actuate the piston l2 therein. Heretofore, anything performing the function of the diaphragm l4 has been of special construction, which will hold air. In this construction. the diaphragm may be pervious or porous as cloth or canvas, as the only function it has to perform is to hold the momentary impulse of air to operate the master valve, the holding of the master valve in its operated position'being performed by the locking means to be presently described.

The master valve locking means includes a pressure chamber 21 and a valve 28 of the mushroom type therein having its stem 29 connected to the diaphragm l4 by a lostmotion, or pinand-slot connection at 38, the stem having a shoulder abutting against a reinforcing disk 3| for the diaphragm similar to the disk H. The valve 28, although it does .not engage the sides of the chamber 21 but is spaced therefrom, nevertheless acts a a piston valve, or is pressureoperated, due to unequal pressures on opposite sides thereof. The valve 28 has an annular flange 32, the edge 33 of which coacts with the valve seat 34, at the bottom of the chamber concen- I trio with the stem 29. The stem slidingfits a bore at the bottom of the chamber. ferential pressure is due to an exhaust 38 to the outer air and opening in the bottom of the chamber 21 within the valve seat 34. The pressure chamber 21 is connected by a pipe 31 to the port H. The air is released from the pressure chamber 27 by a normally-closed, manually-operable release valve 38 connected by a pipe 39 to the chamber 27, it being here shown as connected to the pipe 31 which is a combined intake and exhaust pipe.

In operation, when the two hand control manuals 38 are operated, the air passing from the main line 1 through the two hand control valves 2| and pipe to the diaphragm chamber I 5 actuates the diaphragm l4 from the position shown in Figure 1 to that shown in Figure 2, and in so doing first takes up the lost motion at 30, and then moves'the lock valve 28 down lightly on its seat 34. This operation of the diaphragm l4 also operates the master valve to open the intake valve head 4 and close the exhaust valve head 5, the motion of the diaphragm being transferred through the spring l8. Thus. air enters the cylinder i8 and actuates the piston l2 therein to effect the operation of the machine. as the clos-- ing of a press. When the piston has traveled a predetermined d stance, as far enough to bring the press into closed position or nearlv closed position, the piston uncovers the port I I. whereby the air from the cylinder l0 passes through the pipe 31 into the pressure chamber 21 and forces the valve 28 tightly against its seat 34. thus holding the master valve in its operated position inde- The d f- 28 may also leak out along the sliding clearance at 48 between the stem 29 and the bore in the bottom of the chamber 21' in which the stem slides, and thence out through the exhaust 38 without building up pressure against the valve 28 in. opposition to the pressure through the pipe 31. To restore the master valve 2 to its normal position, in which the intake head 4 is closed and the exhaust head 5 open, and thus permit the air to exhaust from the cylinder lo, the operator opens the release valve 38, and it is necessary to hold it open only momentarily. The opening of the release valve 38 permits the valve 28 to separate from its valve seat 34, and even though this separation is very slight, it is sufficient to permit the air to exhaust from the chamber 21 through the exhaust 38, before the port I I is uncovered by the piston on the retrograde movement of the piston, or in other words, because of the exhaust 38, a momentary opening of the release valve 28 is sufilcient and prevents resetting of the valve 28 by any back pressure'or pressure built up through the pipe 31 before the piston 12 has passed the port I I on its retrograde movement. Upon the release of air from the chamber 21, the spring 36 will restore the diaphragm l4 to the position shown in Figure 1.

- In Figures 3, 4 and 5, a modified form is shown in which the locking means includes a diaphragm and a different diaphragm or independent of the diaphragm which operates the master valve. In these figures, the master valve, the diaphragm and its chamber for initially operating it and the diaphragm and its chamber for looking it in its operated position are arranged in triangular formation. The master valve is of the same con struction as shown in Figure 1, and the same reference numerals are applied thereto. In Figures 3, 4 and 5, 4| designates the diaphragm, and 42 the diaphragm chamber, corresponding to the diaphragm l4 and diaphragm I5 (Figure 1), and the air controlled by the two hand control enters the diaphragm chamber through pipe 43. The diaphragm 4| acts on a plunger 44 against the action of a spring 45, and this plunger coacts with one arm 48 of a Y-shaped lever pivoted to the triangular formation. The leg 41 of the Y-formation thrusts against head 48 on an abutment 49 corresponding to the abutment l8 in Figures 1 and 2. 50 designates the locking diaphragm, and 5| the diaphragm chamber in which it is located, this chamber being connected through the pipe 52 to the port in the side of the cylinder. The diaphragm 5|] thrusts against the head of a valve 53 which preferably transfers its movement through a spring 54 to a "sliding head 55 telescoping into the stem of the valve 53, the head thrusting against the other arm 56 of the Y-shaped lever, the valve head 53 coacting with a seat 51 in the same Way that the valve 28 coacts with the seat 34 (Figures 1 and 2).

When the two hand control is operated, the air passes through the pipe 43 to the diaphragm chamber 42 actuating the diaphragm 4| therein, which in turn through the plunger 44 actuates the Y-shaped lever to cause the leg 41 thereof to operate the master valve 2 to open the intake head 4 and close the exhaust valve head 5 and thus permit the air to pass from the main line 1 through the master valve and pipe 9 to the cylinder ID to actuate the piston I2 therein. When the pistonpasses the port II in the side of the cylinder, the air passes through the pipe 52 to the diaphragm chamber 5|, actuating the porous or leather diaphragm to press the valve opening of the release valve, the air is instantly released from the diaphragm chamber 5! and any built up or back pressure, before the piston l2 passes the port II in its retrograde movement, passes around the valve 53, which is unseated, and the stem thereof, to the outer air, or an outlet 58 may be provided similar to the outlet 36 (Figure 1). Because of-the looseness of the sliding fit of the stem of the valve 53 in its guide passage, a special outlet as 58 is not necessary.

What I claim is: 1. The combination with a pressure-operated servo-motor and an air supply system therefor; of a master valve for controlling the flow of pressure fluid to the motor, operator-operated means for controlling the opening of the master valve including a pressure-operated device, and operator-releasable, pressure-operated locking means connected in said system and controlled by the servo-motor when actuated a predetermined amount to hold the master valve in its operated position independently of the pressure-operated device, the pressure-operated device including a diaphragm chamber and a diaphragm therein, and the locking means including a poppet valve and a chamber in which it is located having a seat therefor, the poppet valve coacting with the diaphragm to be initially moved thereby toward its seat, the chamber in which the-poppet valve is located being connected in the air system, and the'flow of air thereto being controlled by the servo-motor.

2. The combination with a pressure-operated position independently of the pressure-operated device, the pressure-operated device including a diaphragm chamber and a diaphragm therein, and the locking means including a poppet valve and a chamber in which it is located having a seat therefor, the pop valve coacting' with the diaphragm to be initially moved thereby toward its seat, the chamber in which the poppet valve is located being connected in the air'system and the flow of air thereto being controlled by the servo-motor, the chamber in which the poppet valve works being providedwith an open air outlet from within its valve seat.

servo-motor and an air supply system therefor;

of a master valve for controlling the flow of pressure fluid to the motor, operator-operated means fo controlling the opening of the master valve including a pressure-operated device, and opera tor-releasable, pressure-operated locking means connected in said system and controlled by the servo-motor when actuated a predetermined amount to hold the master valve in its operated position independently of the pressure-operated device, the pressure-operated device including a diaphragm chamber and a diaphragm therein of pervious material to permit the air under pressure to pass therethrough, and the locking means including a poppet valve and a chamber in which it is located having a seat therefor, the poppet valve coacting with the diaphragm to be initially moved thereby toward its seat, the diaphragm chamber being connected in the air system and the flow of air thereto being controlled by the servo-motor, the diaphragm chamber being provided with an open air outlet from within its valve seat.

3. The combination with a pressure-operated servo-motor and an air supply system therefor; of a master valve for controlling the flow of pressure fluid to the motor, operator-operated means for controlling the opening of the master valve including a pressure-operated device, and operator-releasable, pressure-operated locking means connected in said system and controlled by the servo-motor when actuated a predetermined amount to hold the master valve in its operated 4. The combination with a pressure-operated servo-motor and an air supply system therefor; of a master'valve for controlling the flow of pressure fluidto the motor, operator-operated means for controlling the opening of the master valve including a pressure-operated device, and operator-releasable, pressure-operated locking means connected in said system and controlled by the servo-motor y when actuated a predetermined amount to hold the master valve in its operated position independently of the pressure-operated device, the pressure-operated device including a diaphragm chamber and a diaphragm therein, and the locking means including a poppet valve and a chamber in which it is located having a seat therefor, the poppet valve coacting with the diaphragm to be initially moved thereby toward its seat, the chamber in which the poppet valve is located being connected in the air system and the flow of air thereto being controlled by the servo-motor, the diaphragm being constructed to permit the air to pass therethrough after being given an additional operating impulse of air.

5. The combination with a pressure-operated servo-motor and an air supply system therefor; of a master valve for controlling the flow of pressure fluid to the motor, operator-operated means device, the pressure-operated device including a diaphragm chamber and a diaphragm therein, and the locking means including a poppet valve and a chamber in which it is located having a seat therefor, the poppet valve coacting with the diaphragm to be initially moved thereby toward its seat, the chamber in which the poppet valve is located being connected in the air system and the flow of air thereto being controlled by the servo-motor, the chamber in which the poppet valve works being provided with an open air outlet from within its valve seat, the diaphragm being constructed to permit the air to pass therethrough after being given an initial operating impulse of air.

6. The combination with a pressure-operated servo-motor; of a master valve for controlling the flow of pressure fluid to the motor, said valve being of the combined intake and exhaust type with the intake normally closed and the exhaust normally open, operator-operated control means for controlling the operating of the master valve ineluding a pressure-operated device, operatorher, a pressure-operated valve member therein, a combined intake and exhaust pipe for said chamber, and means controlled by the operation of the servo-motor for timing and controlling the flow of pressure fluid to, and the exhaust from, the chamber through said pipe, said chamber having an exhaust independent of the exhaust through said pipe and closed from exhausting from the pressure side of said valve member when said valve member isin its operated position and openable to exhaust air from the chamber immediately upon the initial release of said valve member.

7. The combination with a pressure-operated servo-motor and an air system; of a master valve in said system having a self-releasable movable member of the combined intake and exhaust type, with the intake normally closed and the exhaust open for controlling the flow of pressure fluid to the motor, operator-operated means for controlling the opening of the intake of the master valve,

including a diaphragm chamber having a diaphragm therein, means for transferring the movement of the diaphragm to the movable member of the master valve, operator-operated means for controlling the flow of fluid to the diaphragm chamber on the pressure side of the diaphragm, and operator-releasable, pressureoperated means controlled by the servo-motor to hold the diaphragm and the master valve in its operated position independently of the fluid pressure applied to the diaphragm, the diaphragm being constructed to permit the air under pressure to pass therethrough after the diaphragm has received the initial operating impulse of air.

8. The combination with a pressure-operated servo-motor; of a master valve for controlling the flow of pressure fluid to the motor including a movable, self-returnable member of the combined intake and exhaust type, with the intake normally closed and the exhaust open, operatoroperated means for controlling the operation of the movable member including a diaphragm chamber having a diaphragm therein, means for transferring the movement of the diaphragm to the movable member of the master valve, operator-operated means for controlling the flow of fluid to the diaphragm chamber on the pressure side of the diaphragm, pressure-operated means controlled by the servo-motor to hold the diaphragm and the master valve in its operated position independently of the fluid pressure applied to the diaphragm including a pressure chamber, and a pressure-operated locking valve member inthe chamber and thrusting against the diaphragm, the chamber having a seat for said valve member, the valve member being normally spaced from its seat, a combined intake and exhaust pipe for a pressure fluid communicating with the chamber, the flow therethrough being controlled by the operation of the servo-motor, the chamber having an open exhaust from the side of the valve member on which the valve seat is located, said exhaust being arranged to be closed by the valve member, when seated, to the exhaust of air from the chamber, and operator control means for initially releasing the pressure from said chamber.

9. The combination with a pressure-operated servo-motor and an air supply system therefor; of a master valve for controlling the flow of the pressure fluid to the motor, operator-operated means for controlling the opening of the master valve including a pressure-operated device and operator-releasable, pressure-operated locking means connected in said system and controlled by the servo-motor, when actuated a predetermined amount, to hold the master valve in its operated position independently of the pressureoperated device, said pressure-operated device including a chamber and a movable member therein and the locking means including a poppet valve and a chamber in which it is located having a seat therefor, the poppet valve coacting with the movable member to be initially moved thereby toward its seat, the chamber in which the poppet valve is located being connected in the air system and the flow of air thereto being controlled by the servo-motor.

10. The combination with a pressure-operated servo-motor and an air supply system therefor; of a master valve for controlling the flow of the pressure fluid to the motor, operator-operated means for controlling the opening of the master valve including a pressure-operated device and .operator-releasable, pressure-operated locking means connected in said system and controlled by the servo-motor, when actuated a predetermined amount, to hold the master valve in its operated position independently of the pressureoperated device, said pressure-operated device including a chamber and a movable member therein and the locking means including a poppet valve and a chamber in which it is located having a seat therefor, the poppet valve coacting with the movable member to be initially moved thereby toward its seat, the chamber in which the poppet valve is located being connected in the air system and the flow of air thereto being controlled by the servo-motor, the pressure-operated device having a leak port leading from the pressure side of the movable member.

11. The combination with a pressure-operated servo-motor and an air supply system therefor; of a master valve for controlling the flow of pressure fluid to the motor, operator-operated means for controlling the opening of the master valve including a pressure-operated device, and operator-releasable, pressure-operated locking means connected in said system and controlled by the servo-motor when actuated a predetermined amount to hold the master valve in its operated position independently of the pressure-operated device, the pressure-operated device including a diaphragm chamber and a diaphragm therein, and the locking means including a poppet valve and a chamber'in which it is located having a seat therefor, the poppet valve coacting with the diaphragm chamber to be initially moved thereby toward its seat, the chamber in which the poppet valve is located being connected in the air system, and the flow of air thereto being controlled by th servo-motor, the diaphragm chamber having a pressure-releasing leak opening from the pressure side thereof.

12. The combination with a pressure-operated servo-motor, of a master valve having a sellreturnable movable member, of the combined intake and exhaust type normally arranged with the inlet closed and the exhaust open for controlling the flow of pressure fluid to the motor, operator-operated means for controlling the opening of the intake of the master valve and the said chamber on the pressure side of the movable member therein, and operator releasable means controlled by the servo-motor to hold the movable member in said pressure chamber and the master valve in its operated position, including a release valve coacting with the movable member insaid pressure chamber to be initially moved thereby to closed position, a chamber in which the release valve is located, connected in the air system and the flow of air thereto being v controlled by the servo-motor, and a manuallyoperated valve located to exhaust the air from the release valve chamber, all whereby upon the momentary operation or the manually-operated valve, the release valve is unseated and the pressure fluid continues to exhaust even though the manually-operated valve again closes before the exhausting is completed.

ERNEST DAVIS. 

